Complicated ladies' wristwatch with moon-phase display Ref. 4858 in 18K white gold (left) and yellow gold (right).

This timepiece features a moon-phase display at 4 o'clock and a subsidiary seconds dial at 8 o'clock.
Thanks to an ingenious modification of the manually wound caliber 16-250 movement - the smallest mechanical movement hallmarked with the Geneva Seal - Patek Philippe succeeded in integrating a moon-phase display without increasing the thickness of the watch.
The new Ref. 4858 in white gold features a gray satin strap that matches the guilloched silvery dial while the Ref. 4858 J in yellow gold, launched in 2002, now comes with a brown satin strap tastefully coordinated with the guilloched chocolate dial.